(1) Technical Field
This disclosure relates to the measurement of features contained on manufactured parts using a horizontal beam optical comparator, and more particularly with a method and means for plotting contours of three dimensional shapes that are not in the lenses field of view.
(2) Description of the Related Art
In today's manufacturing environment, most operations employ a blend of new technology with tried and reliable older systems. Many manufacturers feature the well proven easily used horizontal beam optical comparator (HBOC) as an inspection tool of choice. The HBOC has a beam of light traveling horizontally across a motorized, or manually adjusted, horizontal stage. This type of comparator is ideal for heavy parts and shafts held on “V” blocks or between centers. Typical work-pieces include castings, transmission shafts, thread form measurement and fabricated machined parts.
As competition increases in the world market, new and improved measuring tools are vital to enhance product quality as well as reduction of product cost.
Optical comparators, particularly of a type that project a shadow image or an obliquely illuminated image of fabricated parts onto a screen overlaid by a template of the part, have enjoyed widespread acceptance as robust and reliable forms of measurement by providing measurement results in a visual and verifiable form. Differences between projected edge features of the part and one or more tolerance boundaries of the same features inscribed on the templates are readily apparent on a comparator screen.
During inspection of fabricated parts, optical comparators, also called profile projectors, offer a much larger field of view and cause less eye fatigue over long usage. The saying “seeing is believing” is appropriate when referring to all optical comparators, whether being horizontal or vertical beam optical comparators. Since these measurement tools project magnified images onto a glass screen to make two dimensional measurements, a tremendous amount of information about that part can be gathered in a short time simply by looking at its image. Optical comparators project profiles of images that are see-through, other features such as the bottom of deep grooves, or other geometric features, contained on work pieces, that are out of the horizontal viewing plane are not visually accessible with respect to the top surface.
There are many diverse types of image-capturing methods within the prior art and, accordingly, there exist arrangements with a variety of applications including a wide range of sizes. Optical comparators are easier to use than most other optical measuring tools and much more all-encompassing in the market and less expensive than the more complicated coordinate measuring machine. Their versatility, range of capabilities and return on investment make comparators indispensable and integral to any quality plan.
Notwithstanding the previously described state of the art, there still remains a need to increase its measurement capacity so as to be able to expand its capability to 3rd axis measurement without involving complex and expensive image data processing methods.